In the past few years, a considerable number of case reports describing predominantly gastrointestinal, urinogenital, and ophthalmic manifestations of microsporidial infections in AlDS patients have been published. Although anecdotal evidence of the therapeutic efficacy of a number of antimicrobial agents has appeared in the literature, there have been little or no in vitro data to substantiate these claims. Of the principal species of microsporidia that are human pathogens, all but Enterocytozoon bienusi have been propagated in a tissue culture system. However there seems to be little consensus about which culture techniques yield the best results. The initial aim of this project is to develop reliable methods for propagating microsporidia in vitro, including E. bienusi. Once this objective is achieved, we intend to screen potentially useful antimicrobial agents to determine which have deleterious effects on microsporidial replication and if this inhibition is species- specific. Compounds will also be examined for their ability to prevent infection of cell culture monolayers by microsporidia. The ultimate goal is to be able to correlate in vitro susceptibility results with in vivo therapeutic responses to help document the effectiveness of different pharmacologic modalities for treating microsporidial disease. Various laboratory methods will be used to evaluate the effectiveness of antimicrosporidial agents. Quantitation of released spores from established cultures will provide information concerning the effect of agents on microsporidial replication and spore production. Quantitation of microsporidial DNA will provide information about the ability of agents to prevent microsporidial replication within the host cell and the ability of agents to prevent infection of host cells.